In an image forming apparatus such as a laser printer, there has been proposed a process cartridge that is detachably mounted to a main body of the apparatus.
The process cartridge includes a drum cartridge having a photosensitive drum and a developing cartridge that is detachably mounted to the drum cartridge and that has a developing roller.
A shaft of the developing roller (developing roller shaft) is rotatably supported by a developing frame that forms a housing for the developing cartridge. In addition, both end portions of the developing roller shaft protrude outwardly from the developing frame. A developing roller driving gear is attached to a part, of one end portion of the developing roller shaft, which protrudes from the developing frame.
When the developing cartridge is mounted to the drum cartridge and a circumferential surface of the developing roller contacts a circumferential surface of the photosensitive drum, the developing roller is rotated via the developing roller shaft when driving force is input to the developing roller driving gear.
Thereby, developer is supplied from the circumferential surface of the developing roller to the circumferential surface of the photosensitive drum.